1. Field of the Invention
The present invention relates to an electron beam excited plasma system used for the manufacture of semiconductor devices and the like.
2. Description of the Related Art
In an electron beam excited plasma system, a reaction gas is excited by means of an electron beam to generate plasma, and etching or film formation is effected by causing the resulting plasma to act on a semiconductor wafer.
In this system, the plasma as electron beam source is formed by DC discharge, and electrons are extracted from the plasma, accelerated, and introduced into a region in which a specific reaction gas is stored as an ambient gas, The reaction gas is activated by means of the electron beam, whereby high-density plasma is generated. In this system, moreover, a magnetic field is formed along the advancing direction of the electron beam, and the beam is guided by means of this magnetic field.
Described in Published Unexamined Japanese Patent Application No. 64-53422 is a plasma system of a type such that an electric discharge gas is converted into plasma, and electrons extracted from the plasma are accelerated and applied to an etching gas. Disclosed in Published Unexamined Japanese Patent Application NO. 1-105540, moreover, is a plasma system of a type such that an inverse-magnetic field coil is used to cancel a magnetic field which is formed in a region for the conversion of reaction gas into plasma. Disclosed in Published Unexamined Japanese Patent Application No. 1-105539, furthermore, is a plasma system of a type such that an electric field is arranged in order to deflect and diffuse electrons which are introduced into a region for the conversion of reaction gas into plasma.
In the plasma systems of these conventional types, however, the distance between the respective centers of solenoids in an acceleration chamber is adjusted to several hundreds of millimeters, and the bore of an exhaust port which can be set in the acceleration chamber is restricted to 100 mm with respect to the moving direction of the electrons and 200 mm with respect to a direction perpendicular to the electron moving direction, in order that magnetic lines of force, formed by means of the solenoids, define an optimum space for the acceleration of the electrons. Thus, the bore of the exhaust port is so small for the capacity of the acceleration chamber that the exhaust efficiency of a vacuum unit is lowered.
A reaction chamber, which adjoins the acceleration chamber, is kept at an inner pressure of 10.sup.-5 to 10.sup.-3 torrs. In order to keep the inside of the acceleration chamber at a degree of vacuum substantially equal to that of the reaction chamber, e.g., at about 3.times.10.sup.-4 torrs, therefore, evacuation of the acceleration chamber takes a lot of time.
In the worst case, an exhaust efficiency of the acceleration chamber decreases, and as a result, corrosive reaction gas produced in the reaction chamber may possibly be introduced into a plasma generating chamber via the acceleration chamber.
There may be provided an alternative arrangement such that an acceleration chamber and a vacuum unit, which communicates with an exhaust port of the acceleration chamber, are formed of a corrosion-resistant material, the acceleration chamber is elongated in the electron moving direction, and the bore of the exhaust port is increased, in order to prevent corrosive reaction gas from entering a plasma generating chamber which adjoins the acceleration chamber. If the acceleration chamber is made longer with respect to the the electron moving direction, however, the distance of electron transit increases, so that the systems are large-sized. Thus, solenoids surrounding an anode and accelerating electrodes must be increased in diameter in order that magnetic lines of force, formed by means of the solenoids, define an optimum space for the acceleration of the electrons. Accordingly, the conventional type plasma systems are large-sized.
In manufacturing semiconductor devices, it is necessary to secure a uniform processing rate (etching rate or film forming rate) within the plane of an object of processing as one of processing characteristics. Since the diameter of modern semiconductor wafers tends to increase from 6 inches to 8 or 12 inches, in particular, the plasma systems are expected to ensure a uniform processing rate for a wider region. According to the conventional systems, however, high-energy electrons concentrate upon the central region of each semiconductor wafer, so that the processing rate takes one value for the central region and another for the peripheral region.